1. Field of the Invention
The present invention relates to the field of downhole fluid analysis in hydrocarbon producing wells. More particularly, the present invention relates to a method and apparatus for determining fluid density, viscosity, and other parameters using a flexural mechanical resonator downhole in a borehole during monitoring while drilling or wire line operations.
2. Background of the Related Art
There is considerable interest in obtaining density and viscosity for formation fluids downhole at reservoir conditions of extreme temperature and pressure during formation sampling, production or drilling. Numerous technologies have been employed toward the end of measuring density and viscosity of liquids downhole. U.S. Pat. No. 6,182,499 discloses a system and method for characterization of materials and combinatorial libraries with mechanical oscillators. U.S. Pat. No. 5,734,098 discloses a method for monitoring and controlling chemical treatment of petroleum, petrochemical and processes with on-line quartz crystal microbalance sensors. The '098 method utilizes thickness shear mode (TSM) resonators, which simultaneously measure mass deposition and fluid properties such as viscosity and or density of a fluid. U.S. Pat. No. 6,176,323 discloses drilling systems with sensors for determining properties of drilling fluid downhole. The '323 patent discloses a plurality of pressure sensors at different depths to determine the fluid gradient.
U.S. Pat. No. 5,741,962 discloses a method and apparatus for analyzing a formation fluid using acoustic measurements. The '962 patent device acoustically determines density and compressibility from acoustic impedance and sound speed. U.S. Pat. No. 5,622,223 discloses a method and apparatus for formation fluid samples utilizing differential pressure measurements. The '223 patent discloses an apparatus that provides two pressure gauges at different depths to determine density from a fluid pressure gradient. U.S. Pat. No. 5,006,845 uses differential fluid pressure at two depths to determine fluid density. U.S. Pat. No. 5,361,632 discloses a method and apparatus for determining multiphase hold up fractions using a gradiometer and a densiometer to provide a pressure gradient to determine fluid density. U.S. Pat. No. 5,204,529 discloses a method and apparatus for measuring borehole fluid density, formation density and or borehole diameter using back-scattered gamma radiation to determine fluid density.
Flexural mechanical resonators have used in the laboratory has for rapid characterization of large numbers of fluid samples. See L. F. Matsiev, Application of Flexural Mechanical Resonator to High Throughput Liquid Characterization, 2000 IEEE International Ultrasonics Symposium, Oct. 22-25, 2000 San Juan, Puerto Rico, incorporated herein by reference in its entirety; L. F. Matsiev, Application of Flexural Mechanical Resonator to High Throughput Liquid Characterization, 1999 IEEE International Ultrasonics Symposium, October 17-20, Lake Tahoe, Nev., incorporated herein by reference in its entirety; L. F. Matsiev, Application of Flexural Mechanical Resonator to High Throughput Liquid Characterization, 1998 IEEE International Ultrasonics Symposium, Oct. 5-8, 1998, Sendai, Miyagi, Japan, incorporated herein by reference in its entirety.
There is, however, no method or apparatus for measuring viscosity in the downhole environment. Moreover, the inventor is aware of no known method or apparatus utilizing a flexural mechanical resonator to determine density, viscosity or other fluid properties in a downhole environment. Thus, there is a need for a method and apparatus utilizing a flexural mechanical resonator to determine density, viscosity or other fluid properties in a downhole environment.